menuentry "Ubuntu ISO" {
  set isofile="/lubuntu-15.04-desktop-i386.iso"
  loopback loop $isofile
  set gfxpayload=keep
  linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile console=tty0 noprompt --
  initrd (loop)/casper/initrd.lz
}